HOWMEDIUM VOLTAGE

METALCLAD SWITCHGEAR HAS

EVOLVED (VD4 & UNIGEAR)

UNIGEAR MODEL

INDOOR AIR INSULATED SWITCHGEAR

Vacuum Solution

• UniGear ZS1 with VD4/Vmax upto 12KV application

• UniGear ZS2 with VD4 36 for 36KV application

UNIGEAR PANEL TYPE

• Single Busbar standard depth deeper version Floor rolling

version• Double Busbar

version• Unigear ZS2 for

36KV

UNIGEAR –SINGLE BUSBAR

Rated Voltage (kV) 12 12 12Dry Power frequency

High Voltage (kV)28 28 28

Impulse withstand Voltage(kVpk)

75 75 75

Rated Frequency (Hz) 50 50 50 Rated Current of Main

Busbar (A)630 to 1250 1250 to

20002500 to

3150/4000 Rated Short- Time

withstand current (kA)26.3/3 sec 26.3/44/3

sec44/3sec

Peak withstand Current (kApk)

66 66/110 110

Rated current of circuit breaker (A)

630 to 1250 630 to 2000 2500 to 3150

UNIGEAR ZS1- DOUBLE BUSBAR

ZS2

Rated Voltage 12 36Impulse withstand

Voltage(kVpk)75/95 75/95

Rated Frequency (Hz) 50 50

Rated Current of Main Busbar (A)

1250 to 3150 2000/2500

Rated Short- Time withstand current (kA)

44/3Sec 31.5/3Sec

Peak withstand Current (kApk) 66 54

Rated current of circuit breaker (A)

1250 to 3150 2000/2500

UNIGEAR PANEL COMPONENTS

1. Low Voltage Compartment2. Gas exhaust duct3. Busbar Compartment 4. Feeder Compartment 5. Circuit breaker6. Circuit breaker

Compartment 7. Withdrawable voltage

transformer with fuses

UNIGEAR FEATURES

Use of Alu-Zinc coating instead of conventional paint, making it more environmental friendly.

Internal arc proof with 1Sec. Test duration

Self supported, Busbar design without conventional support insulator.

Specialized design/construction of cubicles CBs, Busbar, PTs

PANEL INTERNAL INTERLOCKING Circuit breaker can only be moved from the test

position when both the CB and Earthing switch are off.

CB can only be switched ON when breaker is in the test or service position.

CB rack IN/OUT is possible only when there is supply to control plug.

Earth switch can be closed only if the circuit breaker is in test position.

Connecting & Disconnecting of the control plug is only possible in the CB test position.

If the Earthing switch is ON, the CB cannot be moved from the test to service position.

THE ADVANTAGES BROUGHT BY UNIGEAR

• It is aimed at making AIS more compact and better customization over a varied range of voltage & current.

• It uses tubular bus bars which requires less phase clearance compared to rectangular bus bars.

• It has reduced the use of insulators thereby greatly reducing the chance of insulator tracking.

• It is also emphasizing on the use of voltage detecting insulators which can act as a direct replacement of PT.

• It has an improved external earthing truck, with more refined interlock.

BRIEF HISTORY OF VACUUM CIRCUIT BREAKER

1. Vacuum switching technology was developed originally in the USA in the 1920’s but remained non-viable until the late 1940’s and early 1950’s.

2. English Electric created an almost perfect material with the invention of CLR Chrome copper contact material, patented in 1970.

3. Slowly came the improvement in the interrupter construction, its manufacturing and arc control technique.

4. The market for vacuum circuit breakers finally came to prominence from early 1970’s

ARC QUENCHING INSIDE VACUUM INTERRUPTER

• At the instant of de-touching of contacts in a vacuum, the increased current density make the metal on the contact surface easily vaporize and create a conducting media for arc path. The arc gets initiated and continues until the next current zero.

• At current zero the arc is extinguished and the conducting metal vapour is re-condensed on the contact surface.

• At this point, the transient recovery voltage that develops cannot create the electron avalanche necessary to attain the breakdown voltage of the vacuum. Thus, the arc cannot be re established again after current zero.

VD4 VACUUM CIRCUIT BREAKER

A LOOK AT THE PROS AND CONS OF VACUUM SWITCHING

• Vacuum switching has the most effective arc quenching ability and a low life cycle cost upto 52 KV.

• It is more environment friendly and practically maintenance free.

• It is effective in tackling the problem of current chopping.

• VCB uses Butt type contact with CuCr as the contact material because of its good electrical and mechanical properties. CuCr is also resistant to solid welding that may otherwise occur at load closing or short circuit conditions.

• Vacuum medium has an effective dielectric ceiling of 500 KV which roughly corresponds to LIWL of 132 kV voltage medium.

• Beyond 132 KV chances of X-Rays emission from the vacuum interrupters cannot be ruled out.

• High contact pressure upto 600 daN for fault level of 50 KA may be required to prevent popping.

• It is to monitor the condition of the vacuum. A pressure of 10^-4 to 10^-8 mbar must be maintained.

VD4 INTERRUPTER• In the circuit-breaker of type

VD4,the complete pole and the maintenance freevacuum interrupter form a positive unit.

• This is achieved by a specially developed casting technique in which the vacuum interrupter isdirectly embedded in epoxy resin to form a complete pole.

• Disruptive external effects on the switching element are thereforeextensively precluded.

• For very high rated currents, rated short-circuit breaking currents and for rated voltages upto 36 kV, they are used

• The contact gap of only 12 mm is sufficient to provide high dielectric strength.

Arc Control technique1. There can be two types of arc that can develop

inside a vacuum Interrupter the Diffused arc and the Constricted arc.

2. The diffused arc is a natural outcome for fault current upto 10 KA whereas constricted arc appears above 10 KA fault current.

3. In diffused arcing the arcs are uniformly distributed over the entire contact surface whereas in constricted arcing the arc tends to localize on a certain spot causing damage to the interrupter contacts.

4. The objective of arc control technique is to prevent formation of constricted arcing and keep diffused arcing irrespective of the fault current vale.

5. This is achieved by developing either a Radial Magnetic Field or Axial Magnetic Field around the arc using the arc current.

6. VD4 uses Radial Magnetic Field as arc control technique.

VD4 KEY ASPECTS AND STRENGTHS• Application where space saving is a premium

• The panel contacts are mounted in the bushing and the metallic shutters are provided hence, better compartmentalization is achieved.

• Higher reliability and availability and longer life with fewer fastening parts.

• It has moulded case design protecting the vacuum interrupters from impact, dust, and condensation.

• High dielectric protection of the vacuum interrupters without additional modifications.

• VD4 with manual mechanism is suitable for auto reclosing.• It has only one type of operating mechanism (EL) for all the VD4

variants.

FIELD OF APPLICATIONS

Vacuum circuit-breaker of type VD4 is designed for switching:

• Power Transmission and distribution substations

• Motor control and protection

• Capacitor bank control and protection

• Transformers and Generators under load and no-load conditions

• Cables and overhead lines under load and no-load conditions

FEATURES & OVERVIEW• Vacuum interruption technique• Contacts in vacuum protected against oxidation and

contamination • Sealed for life vacuum interrupters

• In accordance with IEC 62271-100 STDs

• Operation sequence O - 0.3” - CO - 15” - CO• Limited switching energy• 10,000 mechanical operations• Stored energy operating mechanism with built-in anti-

pumping device and closing spring charging lever • Insulating monobloc• Operating mechanism and monobloc fixed to a sturdy

metal frame• Easy customization with a complete range of accessories• Locks to prevent incorrect and hazardous operations

VD4 - OVERVIEWOpen/close aux. contacts (standard set of ten aux.c.)

Additional opening release

Locking magnet in the actuator

Opening pushbutton

Closing pushbutton

Shunt tripping release

Built-in lever for closing spring manual charging

Undervoltage release (missing in the picture)

Shunt closing release

Signaling device for closing springs charged/discharged

Mechanical operation counter

Geared motor for closing spring charging

VD4 - STANDARD EQUIPMENT•Mechanical signalling device for CB open/closed

•Mechanical signalling device for closing spring charged/discharged

•Opening and closing pushbuttons

•Mechanical operation counter

•Built-in lever for manually charging of closing spring

•Anti-pumping mechanical built-in function

•5 + 5 auxiliary contacts

•Connection terminals and terminal board for auxiliary circuits (for fixed CB)

•Isolating contacts, cord with connector (plug only), racking-in/out lever (for withdrawable CB)

Brief view of Interrupter structure

1. The Vacuum Interrupter is housed inside a ceramic porcelain cylinder having Alumina 94% and Silica 6%.

2. The Shield is made of oxygen free Copper and is primarily used to capture the metal vapour produced during arcing thereby maintaining the internal insulation of the ceramic porcelain cylinder.

3. The shield also prevents direct exposure from the high fault current/arc.

4. The bellows allow the motion of the movable contact while maintaining vacuum tight seal where the speed of the movable contact reaches from 0 to 2 m/s in less than 100 micro second.

5. The impulse motion parted to the bellows are non uniform and anti twist bushings are provided to improve the mechanical strength of the bellows.

Vacuum Circvuit Breaker type VD-4Rated Voltage KV 12 17.5 36 40.5

Rated Current A 1250 - 2500 3150 - 4000 1250-2500

3150-4000

1250-3150

1250-3150

Rated Short Circuit

Symmetrical current

breaking capacity

KA 40 50 53 20-50 63 40 20-40 25-40 25-31.5

Rated Short Circuit

Asymmetrical current

breaking capacity

KA 43.6 56.8 66.5 21.7-56.8 65.6 43.6 21.7-

43.621.7-43.6

27.3-34.3

Rated Short Circuit Making

current capacity

KA 100 125 158 30-125 158 100 50-100 63-100 63-80

Rated Short Circuit

DurationSEC 3 3 3 3 3 3 3 3 3

ADVANTAGES OF VD4 WITH RESPECT TO HCA• The reduced dimensions of the VCB enables to provide a

very compact air insulated switchgear panel that can rival a gas insulated switchgear.

• The vacuum interrupters are enclosed inside epoxy resin insulators making it more safe and versatile for indoor as well as outdoor use.

• The breakers are customized to be floor mounted or cassette mounted however mostly cassette mounted breakers are used which eliminates the dependency on floor level.

• The cassette mounted VD4 breakers has electrical interlock which ensures that rack in / rack out operations are not possible without control supply.

• It forms the basis of Unigear in which the metering+ relay module, breaker module and line PT can be clubbed into a single compartmentalized cubicle.

• VD4 weighs around 125 to 150 kg and is lighter than HCA type Breakers weighing approximately 190 kg.